2.0 Analysis 2.1 General The attitude of the aircraft at impact indicates that it was out of control at the time of impact. Therefore, the analysis concentrates on those areas that could have led to the loss of control: the pilot's ability to perform, aircraft airworthiness, and environmental issues. 2.2 Pilot Ability to Perform 2.2.1 Medical Incapacitation and Fatigue No pre-existing condition was found in the pilot's aviation medical examinations to suggest the possibility of pre-impact incapacitation. The pilot had 16hours off duty prior to the work period, reporting for work at 1700, with the accident occurring at approximately 2130. This schedule does not raise concerns about chronic or acute fatigue. No information was gathered that indicates that pilot incapacitation or fatigue played a role in this occurrence. 2.2.2 Spatial Disorientation At some point during or shortly after the turn to base leg, the aircraft left controlled flight. The orientation of the aircraft at impact would be consistent with a fully developed aerodynamic stall, with a wing and nose drop. Therefore, the potential for spatial disorientation to have played a role in the aircraft departing controlled flight must be considered. The pilot of the accident aircraft, holding a commercial licence and valid instrument rating, would have been aware of the possibility of such illusions and had been trained to focus attention on the instruments when such illusions were probable or suspected. At the time of the occurrence, some outside visual references were available to help orient the pilot. Although the overcast would have obscured any stars, ground lights from Summer Beaver and the airport itself would have been visible. These ground references would have been off the right side of the aircraft during the downwind leg and off the nose and front right quarter once established on the base leg. Having flown en route at night to Summer Beaver over uninhabited and unlit terrain, and under an overcast sky, the pilot would have been making the transition from flying with reference to the flight instruments to flying with reference to external landmarks at the time control of the aircraft was lost. With the availability of both instruments and external references to help the pilot maintain orientation for the approach and landing, it is difficult to envision how a visual or vestibular illusion, in isolation, could have led to loss of control of the aircraft. The pilot's disorientation would have had to have been significant enough to result in a fully developed stall or spiral dive. Assuming no load or gust factor, and given the target airspeed of 120KIAS on the base leg, the aircraft would have had to lose more than 60knots airspeed to reach the point of the stall. Further, the stall characteristics of the Cessna208B have been described as being fairly docile with adequate warning of an impending stall. Prior to reaching the point of stall, the pilot would have been confronted with a significantly increased nose-up attitude, decreased cockpit noise, decreasing airspeed, a stall warning horn and, finally, buffeting prior to departing controlled flight. Having flown the trip from Pickle Lake with few ground references, the pilot would likely have been sufficiently attentive to his instruments to detect some or all of these symptoms of an approaching stall. The availability of ground references, the pilot's instrument flying experience, and the flying characteristics of the Cessna208B all serve to reduce the probability of spatial disorientation by itself as leading to a loss of control of the aircraft. However, the possibility of disorientation in conjunction with some other event cannot be ruled out. Events such as an in-flight emergency, a failure of the attitude indicator, or an inadvertent entry into a rain shower are all possibilities that might have contributed to pilot spatial disorientation and could not be ruled out in this investigation. 2.2.3 Birdstrike Hazard It is plausible that a birdstrike during the turn to base leg, or shortly thereafter, could have incapacitated the pilot to the extent that subsequent control inputs, or the lack thereof, resulted in loss of control. No bird remains were found at the accident site; however, the intense post-crash fire could have destroyed all evidence of a birdstrike. 2.3 Aircraft Airworthiness 2.3.1 Engine and Propeller The investigation revealed that the engine was developing significant power at impact. Therefore, a lack of engine/propellor power is not considered a contributing factor. 2.3.2 Flight Controls In view of the service bulletins and airworthiness directives associated with the flap system of this aircraft through its history, the investigators conducted a thorough analysis of all the associated flap control systems. All the bellcranks, pulleys, and associated cables that were examined were either normal or were shown to have failed in overload during the crash sequence. The flap tracks and associated rollers showed indicating marks at the 20position, but these marks could have been caused by repeated movement of the flaps to that position through normal flight operation. Exact flap position immediately prior to impact could not be determined as both sections were driven up past the 0 position during the crash. 2.3.3 Structural Failure All the major components of the aircraft were found at the site. The wings were in one piece, and both elevator horns and parts of the elevator were attached to the structure. Ailerons, flaps, and trims were all attached and identified. The cockpit and passenger doors were confirmed as having been closed, and both handles were recovered in the latched position. Therefore, structural failure of a primary control or surface has been eliminated. 2.3.4 Flight Instruments Numerous recurring defects pertaining to the KI256FCI on the operator's Cessna208B Caravan have been documented. Such failures can be very insidious, causing the pilot to become easily disoriented when he realizes that things are not as he perceives them. Such an in-flight emergency would be aggravated in conditions of little or no external visual references. The FCI was fire damaged to the extent that its serviceability could not be determined. However, it is possible that a failure of the FCI, coupled with spatial disorientation or the illusion possibilities described above, could have led to the loss of control. 2.4 Weather Considering the pilot's experience, the ceiling and visibility were adequate for the flight to be conducted under VMC in a safe manner. Rain showers had been forecast and reported throughout the area, but there were no showers observed at the Summer Beaver aerodrome at the time of the aircraft's arrival. The Summer Beaver airport does not have a recorded weather capability, but strong, gusty winds were reported by pilots flying in the area. However, the turbulence was reported only as moderate with no windshear. Although it does not appear that wind was a factor in this accident, the possibility of a localised severe condition cannot be ruled out. 3.0 Conclusions 3.1 Findings as to Causes and Contributing Factors The aircraft departed controlled flight and struck terrain for undetermined reasons. 3.2 Findings as to Risk The company's flight-following procedures for flights operating in remote areas were impractical and were not consistently applied; this could compromise timely search and rescue operations following an accident. 3.3 Other Findings The aircraft did not carry flight recorders. Lack of information about the cause of this accident affects TSB's ability to identify related safety deficiencies and to issue safety communications intended to prevent accidents that could occur under similar circumstances. 4.0 Safety Action 4.1 Action Taken 4.1.1 Flight Instruments The operator has provided maintenance personnel with additional training for handling gyro instruments. 4.1.2Emergency Locator Transmitter Maintenance Requirements The operator has revised its tracking of emergency locator transmitter maintenance requirements. 4.1.3 Flight Following Capability Prior to the accident, the company had started to equip their aircraft with an automatic tracking system. This system updates aircraft position every three minutes and allows operations dispatchers to track the location of an aircraft throughout the duration of its flight. Since the accident, this modification has been completed on all but two of the company's aircraft. 4.1.4 Crew Requirements on Passenger Flights Although not required by regulation, the company has instituted a policy of crewing all passenger flights with two pilots.